The origin of the principle "Lex Orandi, Lex Credendi" questioned

Recently the following piece was brought to my attention. I've only had the opportunity to skim the piece so far, and while it is bound to stir up some controversy, I think it is worth throwing out there in the spirit of academic discussion.

Back in 2004, Dr. Daniel Van Slyke, then a professor at Ave Maria University, wrote an article for Josephinum: Journal of Theology, entitled Lex orandi lex credendi: Liturgy as Locus Theologicus in the Fifth Century? wherein he questions whether our understanding of Prosper of Aquitaine's saying, "ut legem credendi lex statuat supplicandi", which has been "transmogrified" into the more well known axiom, "lex orandi, lex credendi", is in fact representative of Prosper's original intention. In short, does he intend to specifically refer to the liturgy?

To give you some context, I've met Dr. Van Slyke. He is a good man and one whom loves the sacred liturgy. He's also part of the Society for Catholic Liturgy and the Research Institute for Catholic Liturgy who recently hosted Dr. Alcuin Reid in an excellent liturgical conference. When you read this piece, read it bearing this in mind, for as I say, he thesis is challenging some very fundamental thoughts about the meaning of this saying from Prosper of Aquitaine's perspective at any rate.

Having met Dr. Van Slyke, I do not believe he would deny the importance of the form of the sacred liturgy and its effect on our belief, nor that it should reflect our doctrine, however, as a scholar he is questioning whether or not this principle actually comes from Prosper of Aquitaine, or is ultimately a later development in our understanding of the relationship of doctrine and liturgy. In so doing, he is also questioning Pius XII's use of it in Mediator Dei.

It is a long piece, so I will merely link to it above for your discussion.